/*
 * Copyright (c) 1997, 2012, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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package java.util;

/**
 * This class provides a skeletal implementation of the {@link List}
 * interface to minimize the effort required to implement this interface
 * backed by a "random access" data store (such as an array).  For sequential
 * access data (such as a linked list), {@link AbstractSequentialList} should
 * be used in preference to this class.
 *
 * <p>To implement an unmodifiable list, the programmer needs only to extend
 * this class and provide implementations for the {@link #get(int)} and
 * {@link List#size() size()} methods.
 *
 * <p>To implement a modifiable list, the programmer must additionally
 * override the {@link #set(int, Object) set(int, E)} method (which otherwise
 * throws an {@code UnsupportedOperationException}).  If the list is
 * variable-size the programmer must additionally override the
 * {@link #add(int, Object) add(int, E)} and {@link #remove(int)} methods.
 *
 * <p>The programmer should generally provide a void (no argument) and collection
 * constructor, as per the recommendation in the {@link Collection} interface
 * specification.
 *
 * <p>Unlike the other abstract collection implementations, the programmer does
 * <i>not</i> have to provide an iterator implementation; the iterator and
 * list iterator are implemented by this class, on top of the "random access"
 * methods:
 * {@link #get(int)},
 * {@link #set(int, Object) set(int, E)},
 * {@link #add(int, Object) add(int, E)} and
 * {@link #remove(int)}.
 *
 * <p>The documentation for each non-abstract method in this class describes its
 * implementation in detail.  Each of these methods may be overridden if the
 * collection being implemented admits a more efficient implementation.
 *
 * <p>This class is a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.
 *
 * @author Josh Bloch
 * @author Neal Gafter
 * @since 1.2
 */

public abstract class AbstractList<E> extends AbstractCollection<E> implements List<E> {

  /**
   * Sole constructor.  (For invocation by subclass constructors, typically
   * implicit.)
   */
  protected AbstractList() {
  }

  /**
   * Appends the specified element to the end of this list (optional
   * operation).
   *
   * <p>Lists that support this operation may place limitations on what
   * elements may be added to this list.  In particular, some
   * lists will refuse to add null elements, and others will impose
   * restrictions on the type of elements that may be added.  List
   * classes should clearly specify in their documentation any restrictions
   * on what elements may be added.
   *
   * <p>This implementation calls {@code add(size(), e)}.
   *
   * <p>Note that this implementation throws an
   * {@code UnsupportedOperationException} unless
   * {@link #add(int, Object) add(int, E)} is overridden.
   *
   * @param e element to be appended to this list
   * @return {@code true} (as specified by {@link Collection#add})
   * @throws UnsupportedOperationException if the {@code add} operation is not supported by this
   * list
   * @throws ClassCastException if the class of the specified element prevents it from being added
   * to this list
   * @throws NullPointerException if the specified element is null and this list does not permit
   * null elements
   * @throws IllegalArgumentException if some property of this element prevents it from being added
   * to this list
   */
  public boolean add(E e) {
    add(size(), e);
    return true;
  }

  /**
   * {@inheritDoc}
   *
   * @throws IndexOutOfBoundsException {@inheritDoc}
   */
  abstract public E get(int index);

  /**
   * {@inheritDoc}
   *
   * <p>This implementation always throws an
   * {@code UnsupportedOperationException}.
   *
   * @throws UnsupportedOperationException {@inheritDoc}
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException {@inheritDoc}
   * @throws IllegalArgumentException {@inheritDoc}
   * @throws IndexOutOfBoundsException {@inheritDoc}
   */
  public E set(int index, E element) {
    throw new UnsupportedOperationException();
  }

  /**
   * {@inheritDoc}
   *
   * <p>This implementation always throws an
   * {@code UnsupportedOperationException}.
   *
   * @throws UnsupportedOperationException {@inheritDoc}
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException {@inheritDoc}
   * @throws IllegalArgumentException {@inheritDoc}
   * @throws IndexOutOfBoundsException {@inheritDoc}
   */
  public void add(int index, E element) {
    throw new UnsupportedOperationException();
  }

  /**
   * {@inheritDoc}
   *
   * <p>This implementation always throws an
   * {@code UnsupportedOperationException}.
   *
   * @throws UnsupportedOperationException {@inheritDoc}
   * @throws IndexOutOfBoundsException {@inheritDoc}
   */
  public E remove(int index) {
    throw new UnsupportedOperationException();
  }

  // Search Operations

  /**
   * {@inheritDoc}
   *
   * <p>This implementation first gets a list iterator (with
   * {@code listIterator()}).  Then, it iterates over the list until the
   * specified element is found or the end of the list is reached.
   *
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException {@inheritDoc}
   */
  public int indexOf(Object o) {
    ListIterator<E> it = listIterator();
    if (o == null) {
      while (it.hasNext()) {
        if (it.next() == null) {
          return it.previousIndex();
        }
      }
    } else {
      while (it.hasNext()) {
        if (o.equals(it.next())) {
          return it.previousIndex();
        }
      }
    }
    return -1;
  }

  /**
   * {@inheritDoc}
   *
   * <p>This implementation first gets a list iterator that points to the end
   * of the list (with {@code listIterator(size())}).  Then, it iterates
   * backwards over the list until the specified element is found, or the
   * beginning of the list is reached.
   *
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException {@inheritDoc}
   */
  public int lastIndexOf(Object o) {
    ListIterator<E> it = listIterator(size());
    if (o == null) {
      while (it.hasPrevious()) {
        if (it.previous() == null) {
          return it.nextIndex();
        }
      }
    } else {
      while (it.hasPrevious()) {
        if (o.equals(it.previous())) {
          return it.nextIndex();
        }
      }
    }
    return -1;
  }

  // Bulk Operations

  /**
   * Removes all of the elements from this list (optional operation).
   * The list will be empty after this call returns.
   *
   * <p>This implementation calls {@code removeRange(0, size())}.
   *
   * <p>Note that this implementation throws an
   * {@code UnsupportedOperationException} unless {@code remove(int
   * index)} or {@code removeRange(int fromIndex, int toIndex)} is
   * overridden.
   *
   * @throws UnsupportedOperationException if the {@code clear} operation is not supported by this
   * list
   */
  public void clear() {
    removeRange(0, size());
  }

  /**
   * {@inheritDoc}
   *
   * <p>This implementation gets an iterator over the specified collection
   * and iterates over it, inserting the elements obtained from the
   * iterator into this list at the appropriate position, one at a time,
   * using {@code add(int, E)}.
   * Many implementations will override this method for efficiency.
   *
   * <p>Note that this implementation throws an
   * {@code UnsupportedOperationException} unless
   * {@link #add(int, Object) add(int, E)} is overridden.
   *
   * @throws UnsupportedOperationException {@inheritDoc}
   * @throws ClassCastException {@inheritDoc}
   * @throws NullPointerException {@inheritDoc}
   * @throws IllegalArgumentException {@inheritDoc}
   * @throws IndexOutOfBoundsException {@inheritDoc}
   */
  public boolean addAll(int index, Collection<? extends E> c) {
    rangeCheckForAdd(index);
    boolean modified = false;
    for (E e : c) {
      add(index++, e);
      modified = true;
    }
    return modified;
  }

  // Iterators

  /**
   * Returns an iterator over the elements in this list in proper sequence.
   *
   * <p>This implementation returns a straightforward implementation of the
   * iterator interface, relying on the backing list's {@code size()},
   * {@code get(int)}, and {@code remove(int)} methods.
   *
   * <p>Note that the iterator returned by this method will throw an
   * {@link UnsupportedOperationException} in response to its
   * {@code remove} method unless the list's {@code remove(int)} method is
   * overridden.
   *
   * <p>This implementation can be made to throw runtime exceptions in the
   * face of concurrent modification, as described in the specification
   * for the (protected) {@link #modCount} field.
   *
   * @return an iterator over the elements in this list in proper sequence
   */
  public Iterator<E> iterator() {
    return new Itr();
  }

  /**
   * {@inheritDoc}
   *
   * <p>This implementation returns {@code listIterator(0)}.
   *
   * @see #listIterator(int)
   */
  public ListIterator<E> listIterator() {
    return listIterator(0);
  }

  /**
   * {@inheritDoc}
   *
   * <p>This implementation returns a straightforward implementation of the
   * {@code ListIterator} interface that extends the implementation of the
   * {@code Iterator} interface returned by the {@code iterator()} method.
   * The {@code ListIterator} implementation relies on the backing list's
   * {@code get(int)}, {@code set(int, E)}, {@code add(int, E)}
   * and {@code remove(int)} methods.
   *
   * <p>Note that the list iterator returned by this implementation will
   * throw an {@link UnsupportedOperationException} in response to its
   * {@code remove}, {@code set} and {@code add} methods unless the
   * list's {@code remove(int)}, {@code set(int, E)}, and
   * {@code add(int, E)} methods are overridden.
   *
   * <p>This implementation can be made to throw runtime exceptions in the
   * face of concurrent modification, as described in the specification for
   * the (protected) {@link #modCount} field.
   *
   * @throws IndexOutOfBoundsException {@inheritDoc}
   */
  public ListIterator<E> listIterator(final int index) {
    rangeCheckForAdd(index);

    return new ListItr(index);
  }

  private class Itr implements Iterator<E> {

    /**
     * Index of element to be returned by subsequent call to next.
     */
    int cursor = 0;

    /**
     * Index of element returned by most recent call to next or
     * previous.  Reset to -1 if this element is deleted by a call
     * to remove.
     */
    int lastRet = -1;

    /**
     * The modCount value that the iterator believes that the backing
     * List should have.  If this expectation is violated, the iterator
     * has detected concurrent modification.
     */
    int expectedModCount = modCount;

    public boolean hasNext() {
      return cursor != size();
    }

    public E next() {
      checkForComodification();
      try {
        int i = cursor;
        E next = get(i);
        lastRet = i;
        cursor = i + 1;
        return next;
      } catch (IndexOutOfBoundsException e) {
        checkForComodification();
        throw new NoSuchElementException();
      }
    }

    public void remove() {
      if (lastRet < 0) {
        throw new IllegalStateException();
      }
      checkForComodification();

      try {
        AbstractList.this.remove(lastRet);
        if (lastRet < cursor) {
          cursor--;
        }
        lastRet = -1;
        expectedModCount = modCount;
      } catch (IndexOutOfBoundsException e) {
        throw new ConcurrentModificationException();
      }
    }

    final void checkForComodification() {
      if (modCount != expectedModCount) {
        throw new ConcurrentModificationException();
      }
    }
  }

  private class ListItr extends Itr implements ListIterator<E> {

    ListItr(int index) {
      cursor = index;
    }

    public boolean hasPrevious() {
      return cursor != 0;
    }

    public E previous() {
      checkForComodification();
      try {
        int i = cursor - 1;
        E previous = get(i);
        lastRet = cursor = i;
        return previous;
      } catch (IndexOutOfBoundsException e) {
        checkForComodification();
        throw new NoSuchElementException();
      }
    }

    public int nextIndex() {
      return cursor;
    }

    public int previousIndex() {
      return cursor - 1;
    }

    public void set(E e) {
      if (lastRet < 0) {
        throw new IllegalStateException();
      }
      checkForComodification();

      try {
        AbstractList.this.set(lastRet, e);
        expectedModCount = modCount;
      } catch (IndexOutOfBoundsException ex) {
        throw new ConcurrentModificationException();
      }
    }

    public void add(E e) {
      checkForComodification();

      try {
        int i = cursor;
        AbstractList.this.add(i, e);
        lastRet = -1;
        cursor = i + 1;
        expectedModCount = modCount;
      } catch (IndexOutOfBoundsException ex) {
        throw new ConcurrentModificationException();
      }
    }
  }

  /**
   * {@inheritDoc}
   *
   * <p>This implementation returns a list that subclasses
   * {@code AbstractList}.  The subclass stores, in private fields, the
   * offset of the subList within the backing list, the size of the subList
   * (which can change over its lifetime), and the expected
   * {@code modCount} value of the backing list.  There are two variants
   * of the subclass, one of which implements {@code RandomAccess}.
   * If this list implements {@code RandomAccess} the returned list will
   * be an instance of the subclass that implements {@code RandomAccess}.
   *
   * <p>The subclass's {@code set(int, E)}, {@code get(int)},
   * {@code add(int, E)}, {@code remove(int)}, {@code addAll(int,
   * Collection)} and {@code removeRange(int, int)} methods all
   * delegate to the corresponding methods on the backing abstract list,
   * after bounds-checking the index and adjusting for the offset.  The
   * {@code addAll(Collection c)} method merely returns {@code addAll(size,
   * c)}.
   *
   * <p>The {@code listIterator(int)} method returns a "wrapper object"
   * over a list iterator on the backing list, which is created with the
   * corresponding method on the backing list.  The {@code iterator} method
   * merely returns {@code listIterator()}, and the {@code size} method
   * merely returns the subclass's {@code size} field.
   *
   * <p>All methods first check to see if the actual {@code modCount} of
   * the backing list is equal to its expected value, and throw a
   * {@code ConcurrentModificationException} if it is not.
   *
   * @throws IndexOutOfBoundsException if an endpoint index value is out of range {@code (fromIndex
   * < 0 || toIndex > size)}
   * @throws IllegalArgumentException if the endpoint indices are out of order {@code (fromIndex >
   * toIndex)}
   */
  public List<E> subList(int fromIndex, int toIndex) {
    return (this instanceof RandomAccess ?
        new RandomAccessSubList<>(this, fromIndex, toIndex) :
        new SubList<>(this, fromIndex, toIndex));
  }

  // Comparison and hashing

  /**
   * Compares the specified object with this list for equality.  Returns
   * {@code true} if and only if the specified object is also a list, both
   * lists have the same size, and all corresponding pairs of elements in
   * the two lists are <i>equal</i>.  (Two elements {@code e1} and
   * {@code e2} are <i>equal</i> if {@code (e1==null ? e2==null :
   * e1.equals(e2))}.)  In other words, two lists are defined to be
   * equal if they contain the same elements in the same order.<p>
   *
   * This implementation first checks if the specified object is this
   * list. If so, it returns {@code true}; if not, it checks if the
   * specified object is a list. If not, it returns {@code false}; if so,
   * it iterates over both lists, comparing corresponding pairs of elements.
   * If any comparison returns {@code false}, this method returns
   * {@code false}.  If either iterator runs out of elements before the
   * other it returns {@code false} (as the lists are of unequal length);
   * otherwise it returns {@code true} when the iterations complete.
   *
   * @param o the object to be compared for equality with this list
   * @return {@code true} if the specified object is equal to this list
   */
  public boolean equals(Object o) {
    if (o == this) {
      return true;
    }
    if (!(o instanceof List)) {
      return false;
    }

    ListIterator<E> e1 = listIterator();
    ListIterator<?> e2 = ((List<?>) o).listIterator();
    while (e1.hasNext() && e2.hasNext()) {
      E o1 = e1.next();
      Object o2 = e2.next();
      if (!(o1 == null ? o2 == null : o1.equals(o2))) {
        return false;
      }
    }
    return !(e1.hasNext() || e2.hasNext());
  }

  /**
   * Returns the hash code value for this list.
   *
   * <p>This implementation uses exactly the code that is used to define the
   * list hash function in the documentation for the {@link List#hashCode}
   * method.
   *
   * @return the hash code value for this list
   */
  public int hashCode() {
    int hashCode = 1;
    for (E e : this) {
      hashCode = 31 * hashCode + (e == null ? 0 : e.hashCode());
    }
    return hashCode;
  }

  /**
   * Removes from this list all of the elements whose index is between
   * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
   * Shifts any succeeding elements to the left (reduces their index).
   * This call shortens the list by {@code (toIndex - fromIndex)} elements.
   * (If {@code toIndex==fromIndex}, this operation has no effect.)
   *
   * <p>This method is called by the {@code clear} operation on this list
   * and its subLists.  Overriding this method to take advantage of
   * the internals of the list implementation can <i>substantially</i>
   * improve the performance of the {@code clear} operation on this list
   * and its subLists.
   *
   * <p>This implementation gets a list iterator positioned before
   * {@code fromIndex}, and repeatedly calls {@code ListIterator.next}
   * followed by {@code ListIterator.remove} until the entire range has
   * been removed.  <b>Note: if {@code ListIterator.remove} requires linear
   * time, this implementation requires quadratic time.</b>
   *
   * @param fromIndex index of first element to be removed
   * @param toIndex index after last element to be removed
   */
  protected void removeRange(int fromIndex, int toIndex) {
    ListIterator<E> it = listIterator(fromIndex);
    for (int i = 0, n = toIndex - fromIndex; i < n; i++) {
      it.next();
      it.remove();
    }
  }

  /**
   * The number of times this list has been <i>structurally modified</i>.
   * Structural modifications are those that change the size of the
   * list, or otherwise perturb it in such a fashion that iterations in
   * progress may yield incorrect results.
   *
   * <p>This field is used by the iterator and list iterator implementation
   * returned by the {@code iterator} and {@code listIterator} methods.
   * If the value of this field changes unexpectedly, the iterator (or list
   * iterator) will throw a {@code ConcurrentModificationException} in
   * response to the {@code next}, {@code remove}, {@code previous},
   * {@code set} or {@code add} operations.  This provides
   * <i>fail-fast</i> behavior, rather than non-deterministic behavior in
   * the face of concurrent modification during iteration.
   *
   * <p><b>Use of this field by subclasses is optional.</b> If a subclass
   * wishes to provide fail-fast iterators (and list iterators), then it
   * merely has to increment this field in its {@code add(int, E)} and
   * {@code remove(int)} methods (and any other methods that it overrides
   * that result in structural modifications to the list).  A single call to
   * {@code add(int, E)} or {@code remove(int)} must add no more than
   * one to this field, or the iterators (and list iterators) will throw
   * bogus {@code ConcurrentModificationExceptions}.  If an implementation
   * does not wish to provide fail-fast iterators, this field may be
   * ignored.
   */
  protected transient int modCount = 0;

  private void rangeCheckForAdd(int index) {
    if (index < 0 || index > size()) {
      throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
    }
  }

  private String outOfBoundsMsg(int index) {
    return "Index: " + index + ", Size: " + size();
  }
}

class SubList<E> extends AbstractList<E> {

  private final AbstractList<E> l;
  private final int offset;
  private int size;

  SubList(AbstractList<E> list, int fromIndex, int toIndex) {
    if (fromIndex < 0) {
      throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
    }
    if (toIndex > list.size()) {
      throw new IndexOutOfBoundsException("toIndex = " + toIndex);
    }
    if (fromIndex > toIndex) {
      throw new IllegalArgumentException("fromIndex(" + fromIndex +
          ") > toIndex(" + toIndex + ")");
    }
    l = list;
    offset = fromIndex;
    size = toIndex - fromIndex;
    this.modCount = l.modCount;
  }

  public E set(int index, E element) {
    rangeCheck(index);
    checkForComodification();
    return l.set(index + offset, element);
  }

  public E get(int index) {
    rangeCheck(index);
    checkForComodification();
    return l.get(index + offset);
  }

  public int size() {
    checkForComodification();
    return size;
  }

  public void add(int index, E element) {
    rangeCheckForAdd(index);
    checkForComodification();
    l.add(index + offset, element);
    this.modCount = l.modCount;
    size++;
  }

  public E remove(int index) {
    rangeCheck(index);
    checkForComodification();
    E result = l.remove(index + offset);
    this.modCount = l.modCount;
    size--;
    return result;
  }

  protected void removeRange(int fromIndex, int toIndex) {
    checkForComodification();
    l.removeRange(fromIndex + offset, toIndex + offset);
    this.modCount = l.modCount;
    size -= (toIndex - fromIndex);
  }

  public boolean addAll(Collection<? extends E> c) {
    return addAll(size, c);
  }

  public boolean addAll(int index, Collection<? extends E> c) {
    rangeCheckForAdd(index);
    int cSize = c.size();
    if (cSize == 0) {
      return false;
    }

    checkForComodification();
    l.addAll(offset + index, c);
    this.modCount = l.modCount;
    size += cSize;
    return true;
  }

  public Iterator<E> iterator() {
    return listIterator();
  }

  public ListIterator<E> listIterator(final int index) {
    checkForComodification();
    rangeCheckForAdd(index);

    return new ListIterator<E>() {
      private final ListIterator<E> i = l.listIterator(index + offset);

      public boolean hasNext() {
        return nextIndex() < size;
      }

      public E next() {
        if (hasNext()) {
          return i.next();
        } else {
          throw new NoSuchElementException();
        }
      }

      public boolean hasPrevious() {
        return previousIndex() >= 0;
      }

      public E previous() {
        if (hasPrevious()) {
          return i.previous();
        } else {
          throw new NoSuchElementException();
        }
      }

      public int nextIndex() {
        return i.nextIndex() - offset;
      }

      public int previousIndex() {
        return i.previousIndex() - offset;
      }

      public void remove() {
        i.remove();
        SubList.this.modCount = l.modCount;
        size--;
      }

      public void set(E e) {
        i.set(e);
      }

      public void add(E e) {
        i.add(e);
        SubList.this.modCount = l.modCount;
        size++;
      }
    };
  }

  public List<E> subList(int fromIndex, int toIndex) {
    return new SubList<>(this, fromIndex, toIndex);
  }

  private void rangeCheck(int index) {
    if (index < 0 || index >= size) {
      throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
    }
  }

  private void rangeCheckForAdd(int index) {
    if (index < 0 || index > size) {
      throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
    }
  }

  private String outOfBoundsMsg(int index) {
    return "Index: " + index + ", Size: " + size;
  }

  private void checkForComodification() {
    if (this.modCount != l.modCount) {
      throw new ConcurrentModificationException();
    }
  }
}

class RandomAccessSubList<E> extends SubList<E> implements RandomAccess {

  RandomAccessSubList(AbstractList<E> list, int fromIndex, int toIndex) {
    super(list, fromIndex, toIndex);
  }

  public List<E> subList(int fromIndex, int toIndex) {
    return new RandomAccessSubList<>(this, fromIndex, toIndex);
  }
}
